Mr. Justice Powell
delivered the opinion of the Court.
Petitioner was convicted of federal drug offenses based on evidence seized in January 1971 when Border Patrol officers stopped his camper pickup at a traffic checkpoint on California Highway 86, about 36 air miles from the Mexican border. The officers first determined that petitioner was a United States citizen, then asked him to open the camper so that they could search for concealed aliens. When petitioner opened the door, one officer noticed a strong odor of marihuana. He entered the camper and discovered approximately 356 pounds of the drug. A subsequent search of the passenger compartment produced a number of benzedrine tablets.
The Court of Appeals for the Ninth Circuit affirmed petitioner’s conviction, rejecting his argument that the search was unlawful. 462 F. 2d 347 (1972). A petition for certiorari was pending when we announced our decision in
Almeida-Sanchez
v.
United States,
413 U. S. 266 (1973), holding that the Fourth Amendment prohibits the use of roving patrols to search vehicles, with neither a warrant nor probable cause, at points removed from the border and its functional equivalents. We vacated the judgment in petitioner’s case and remanded for reconsideration in light of
Almeida-Sanchez.
413 U. S. 915 (1973).
The Court of Appeals reheard the case en banc and held, in a sharply divided opinion, that the principles of
Almeida-Sanchez
applied to searches conducted at traffic checkpoints as well as searches conducted by roving patrols. The Court nevertheless affirmed petitioner’s conviction, holding that
Almeida-Sanchez
would not be applied to invalidate searches that occurred prior to the date of that decision. 500 F. 2d 960 (1974). We
granted certiorari to resolve an apparent conflict with the Court of Appeals for the Tenth Circuit in
United States
v.
King,
485 F. 2d 353 (1973), and
United States
v.
Maddox,
485 F. 2d 361 (1973).
We hold today in
United States
v.
Ortiz, ante,
p. 891, that the Fourth Amendment, as interpreted in
AlmeidaSanchez,
forbids searching cars at traffic checkpoints in the absence of consent or probable cause. In this case the Government does not contend that the Highway 86 checkpoint is a functional equivalent of the border, that the officers had probable cause to open the camper, or that petitioner consented to the search. The primary question for decision is whether the principles of
Almeida-Sanchez
should have been applied retroactively.
In
United States
v.
Peltier, ante,
p. 531, we refused to apply
Almeida-Sanchez
to a roving-patrol search conducted before June 21, 1973, even though a direct appeal was pending on that date. We think the decision in
Peltier
is controlling here, as the reasons that dictated a holding of nonretroactivity in that case are equally applicable. At the time of our decision in
Almeida-Sanchez,
all the Courts of Appeals in Circuits adjacent to the Mexican border had held that immigration officers at traffic checkpoints could search automobiles for concealed aliens.
E. g., United States
v.
McCormick,
468 F. 2d 68 (CA10 1972);
United States
v.
De Leon,
462 F. 2d 170 (CA5 1972);
Fumagalli
v.
United States,
429 F. 2d 1011 (CA9 1970) ,
This Court had
not ruled on the question, and no contrary precedent was reported in other Courts of Appeals. The Border Patrol reasonably relied on the decisions of the Court of Appeals in performing the search in this case and others like it, and in these circumstances the purposes of the Fourth Amendment exclusionary rule would not be served by applying the principles of
Almeida-Sanchez
retroactively.
Petitioner further argues that even if
Almeida-Sanchez
is not to be applied retroactively he is entitled to the benefit of the Court of Appeals’ decision that
AlmeidaSanchez
extended to checkpoint searches. He invokes this Court’s practice of applying new constitutional doctrine in the case that establishes the point,
and maintains that the Court of Appeals’ refusal to apply its extension of
Almeida-Sanchez
in his case made its discussion of that point mere dictum. We conclude, however, that the only error of the Court of Appeals was its reaching out to decide that
Almeida-Sanchez
applied to checkpoint searches in a case that did not require decision of the issue.
The Government raised two questions in the Court of Appeals: whether
Almeida-Sanchez
applied retroactively, and if it did, whether it would require probable cause for checkpoint searches. This Court consistently has declined to address unsettled questions regarding the scope of decisions establishing new constitutional doctrine in cases in which it holds those decisions nonretroactive.
E. g., Michigan
v.
Payne,
412 U. S. 47, 49-50 (1973);
DeStefano
v.
Woods,
392 U. S. 631 (1968). This practice is rooted in our reluctance to decide constitutional questions unnecessarily. See
United States
v.
Raines,
362 U. S. 17, 21 (1960);
Ashwander
v.
TV A,
297 U. S. 288, 346-347 (1936) (Brandeis, J., concurring) . Because this reluctance in turn is grounded in the constitutional role of the federal courts,
United States
v.
Raines, supra,
the district courts and courts of appeals should follow our practice, when issues of both retro-activity and application of constitutional doctrine are raised, of deciding the retroactivity issue first. As the
Court of Appeals correctly decided in this case that
Almeida-Sanchez
did not apply to a 1971 search, it should have refrained from considering whether our decision in that case applied to searches at checkpoints.
Petitioner contends, nevertheless, that once the Court of Appeals addressed the unnecessary issue it was bound to apply that ruling in his case. Because it refused to do so, petitioner says the court rendered a hypothetical decision forbidden by Art. Ill of the Constitution. It is true that this Court has suggested that Art. Ill is the primary impetus for applying new constitutional doctrines in cases that establish them for the first time.
Stovall
v.
Denno,
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Mr. Justice Powell
delivered the opinion of the Court.
Petitioner was convicted of federal drug offenses based on evidence seized in January 1971 when Border Patrol officers stopped his camper pickup at a traffic checkpoint on California Highway 86, about 36 air miles from the Mexican border. The officers first determined that petitioner was a United States citizen, then asked him to open the camper so that they could search for concealed aliens. When petitioner opened the door, one officer noticed a strong odor of marihuana. He entered the camper and discovered approximately 356 pounds of the drug. A subsequent search of the passenger compartment produced a number of benzedrine tablets.
The Court of Appeals for the Ninth Circuit affirmed petitioner’s conviction, rejecting his argument that the search was unlawful. 462 F. 2d 347 (1972). A petition for certiorari was pending when we announced our decision in
Almeida-Sanchez
v.
United States,
413 U. S. 266 (1973), holding that the Fourth Amendment prohibits the use of roving patrols to search vehicles, with neither a warrant nor probable cause, at points removed from the border and its functional equivalents. We vacated the judgment in petitioner’s case and remanded for reconsideration in light of
Almeida-Sanchez.
413 U. S. 915 (1973).
The Court of Appeals reheard the case en banc and held, in a sharply divided opinion, that the principles of
Almeida-Sanchez
applied to searches conducted at traffic checkpoints as well as searches conducted by roving patrols. The Court nevertheless affirmed petitioner’s conviction, holding that
Almeida-Sanchez
would not be applied to invalidate searches that occurred prior to the date of that decision. 500 F. 2d 960 (1974). We
granted certiorari to resolve an apparent conflict with the Court of Appeals for the Tenth Circuit in
United States
v.
King,
485 F. 2d 353 (1973), and
United States
v.
Maddox,
485 F. 2d 361 (1973).
We hold today in
United States
v.
Ortiz, ante,
p. 891, that the Fourth Amendment, as interpreted in
AlmeidaSanchez,
forbids searching cars at traffic checkpoints in the absence of consent or probable cause. In this case the Government does not contend that the Highway 86 checkpoint is a functional equivalent of the border, that the officers had probable cause to open the camper, or that petitioner consented to the search. The primary question for decision is whether the principles of
Almeida-Sanchez
should have been applied retroactively.
In
United States
v.
Peltier, ante,
p. 531, we refused to apply
Almeida-Sanchez
to a roving-patrol search conducted before June 21, 1973, even though a direct appeal was pending on that date. We think the decision in
Peltier
is controlling here, as the reasons that dictated a holding of nonretroactivity in that case are equally applicable. At the time of our decision in
Almeida-Sanchez,
all the Courts of Appeals in Circuits adjacent to the Mexican border had held that immigration officers at traffic checkpoints could search automobiles for concealed aliens.
E. g., United States
v.
McCormick,
468 F. 2d 68 (CA10 1972);
United States
v.
De Leon,
462 F. 2d 170 (CA5 1972);
Fumagalli
v.
United States,
429 F. 2d 1011 (CA9 1970) ,
This Court had
not ruled on the question, and no contrary precedent was reported in other Courts of Appeals. The Border Patrol reasonably relied on the decisions of the Court of Appeals in performing the search in this case and others like it, and in these circumstances the purposes of the Fourth Amendment exclusionary rule would not be served by applying the principles of
Almeida-Sanchez
retroactively.
Petitioner further argues that even if
Almeida-Sanchez
is not to be applied retroactively he is entitled to the benefit of the Court of Appeals’ decision that
AlmeidaSanchez
extended to checkpoint searches. He invokes this Court’s practice of applying new constitutional doctrine in the case that establishes the point,
and maintains that the Court of Appeals’ refusal to apply its extension of
Almeida-Sanchez
in his case made its discussion of that point mere dictum. We conclude, however, that the only error of the Court of Appeals was its reaching out to decide that
Almeida-Sanchez
applied to checkpoint searches in a case that did not require decision of the issue.
The Government raised two questions in the Court of Appeals: whether
Almeida-Sanchez
applied retroactively, and if it did, whether it would require probable cause for checkpoint searches. This Court consistently has declined to address unsettled questions regarding the scope of decisions establishing new constitutional doctrine in cases in which it holds those decisions nonretroactive.
E. g., Michigan
v.
Payne,
412 U. S. 47, 49-50 (1973);
DeStefano
v.
Woods,
392 U. S. 631 (1968). This practice is rooted in our reluctance to decide constitutional questions unnecessarily. See
United States
v.
Raines,
362 U. S. 17, 21 (1960);
Ashwander
v.
TV A,
297 U. S. 288, 346-347 (1936) (Brandeis, J., concurring) . Because this reluctance in turn is grounded in the constitutional role of the federal courts,
United States
v.
Raines, supra,
the district courts and courts of appeals should follow our practice, when issues of both retro-activity and application of constitutional doctrine are raised, of deciding the retroactivity issue first. As the
Court of Appeals correctly decided in this case that
Almeida-Sanchez
did not apply to a 1971 search, it should have refrained from considering whether our decision in that case applied to searches at checkpoints.
Petitioner contends, nevertheless, that once the Court of Appeals addressed the unnecessary issue it was bound to apply that ruling in his case. Because it refused to do so, petitioner says the court rendered a hypothetical decision forbidden by Art. Ill of the Constitution. It is true that this Court has suggested that Art. Ill is the primary impetus for applying new constitutional doctrines in cases that establish them for the first time.
Stovall
v.
Denno,
388 U. S. 293, 301 (1967). But petitioner’s case is altogether different.
Almeida-Sanchez
already had established the principle, and there was a genuine controversy between petitioner and the United States over its retroactive application. Contrary to petitioner’s assertion, the court’s jurisdiction to resolve that controversy could not be dislodged by its discussion of an unnecessary issue.
The judgment of the Court of Appeals is
Affirmed.
Me. Justice Douglas dissents for the reasons stated in his dissent in
United States
v.
Peltier, ante,
p. 543.
Mr. Justice Brennan and Mr. Justice Marshall dissent and would reverse substantially for the reasons expressed in Mr. Justice Brennan’s dissent in
United States
v.
Peltier, ante,
p. 544.
Mr. Justice Stewart dissents.